Pre-recorded audio, for example, music, speech, combinations of music and speech such as may occur in advertisements, or other pre-recorded sound, is typically recorded at different sound levels. When playing back pre-recorded audio from different sources, such as occurs when two music tracks from different sources are played back consecutively, the sound volume that is produced by the equipment playing the audio differs according to the level of the original recording. In order to achieve a listening level that is approximately equal for both tracks, a volume control on the equipment must typically be adjusted. For each track, the adjustment can only be made as the track is played, and is normally made by an operator of the equipment adjusting the volume control manually, after a transition from a first to a second track has been made. The need for constantly adjusting the volume control is at the very least annoying.
In audio equipment that allows pre-recorded tracks to be mixed, it is desirable to maintain an approximately equal listening level during the transition, as the level of a first track is reduced and the level of a second track is increased. Because the two tracks will normally be recorded at different levels, both the rate of reduction and the rate of increase may have to be manually adjusted, by an operator of the mixing system as he/she listens to the mixed output, in order to produce an acceptable sound level. In addition, during mixing, constructive and destructive interference effects can significantly affect the final level of sound output from the mixing equipment. Thus, a system which can allow for sound levels to be maintained at a pre-set level, regardless of the track being played or of transitions between tracks, would be advantageous.